In recent years electromechanical types of thermostats using a bimetal as a temperature sensor have been replaced by electronic thermostats. Electronic thermostats presently use a thermistor as a temperature sensor or input. This requires calibration by adjustment of resistors in a bridge circuit. The setpoint is normally provided for this type thermostat by adjusting a variable resistor by moving a mechanical wiper. There is serious concern that the variable resistor used for the setpoint remains stable. The wiping action over a long period of time could possibly change the resistance value and thereby the reliability of the calibration.
Also, the calibration of the thermostat must be sufficiently accurate so that no noticeable discrepancies occur between the control point temperature, and the normal bimetal temperature indicator that is usually used with this type of thermostat.